The present invention relates generally to an improved electrical laminate system, and more specifically to an improved electrical laminate utilizing a substrate having desirable physical, chemical and electrical properties. The substrate comprises, in combination, a woven glass cloth base pad interposed, preferably along the neutral plane, between a pair of outer substrate layers of polyester mat. The glass cloth is a conventional woven glass cloth while the mat layers disposed along the surfaces include a mat of spunbonded continuous filament polyester fibers including primarily fibers having a predominately thermoplastic characteristic with some modest thermoset characteristics, the thermoplastic fibers being utilized to bind the thermoset fibers in place in the mat. The polyester fibers hold the glass cloth out of contact with the electrical conductors.
The laminate structure further includes an impregnating or bonding resin, with the resin being employed to substantially saturate or impregnate the interstices of the laminate in order to provide solvent resistance, mechanical durability, rigidity, and also to enhance the chemical, physical and electrical properties. When a selfextinguishing or flame-retardant product is required, combinations of antimony oxide with highly chlorinated hydrocarbons and/or antimony oxide with brominated compounds may be employed as fillers.
In the preparation of electrical laminate materials, such as those electrical laminate materials which are designed for use as either printed wiring or printed circuitry devices, or the like, it is normally necessary to provide a substrate member between opposed metallic sheet members so as to provide a laminate having sound mechanical and chemical properties, to permit exposure of the structure to manufacturing operations including chemical etching, high temperature soldering and the like, and also to provide a finished product with desirable electrical properties. The substrate material must, therefore have electrical properties including high resistivity, and also proper dielectric strength.
In the past, it has been conventional to provide substrate materials which will provide either a flexible or a rigid laminate substance. For flexible materials, layers of films of stress oriented polyethylene terephthalate, such as that certain film sold by E. I. DuPont deNemours Corporation of Wilmington, Delaware under the name "Mylar" or other thin flexible films have been employed to support one or more surface layers of metallic electrical conductors. These substrate materials have found considerable utility and acceptance in the electrical field.
For rigid circuitry, either single or double-sided, it has been conventional to employ layers of phenolic-glass, phenolic-canvas, or other resinous materials such as epoxy resins with similar reinforcement materials, as well as other combinations to provide a rigid, durable board. Obviously, it is important to control the electrical properties of the supporting substrate so as to render them compatible with the ultimate end application of the laminate.